In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric current to flow through an external circuit. As is further known, the source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air, or any other source of mechanical energy. In practical applications, generators provide nearly all of the power for electric power grids.
As is further known, the reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. Many motors can be mechanically driven to generate electricity and frequently make acceptable generators.
Electrical generators and motors (such as of the AC induction or DC variety) typically include an outer stator (or stationary component) which is usually shaped as a hollow cylinder containing copper wires which are wound or otherwise configured within the inner facing wall. In a motor configured application, electricity flowing into selected pairs of coils configured within the stator (a three phase motor typically includes three individual pairs of coils which are arranged in opposing and partially circumferentially offsetting fashion) results in rotation of an interiorly positioned rotor component.
The rotor is usually shaped as a solid cylinder that sits inside the stator (with a defined air gap between the outer cylindrical surface of the rotor and the inner cylindrical surface of the stator) with an output shaft extending from an axial centerline of the rotor. The rotor further includes a series of highly conductive elements (such as aluminum rods) embedded within its outer surface.
In an electric motor driving application, a separate current is fed to the rods via a commutator which is a mechanism used to switch the input of certain AC and DC machines and which usually includes a plurality of slip ring segments insulated from each other and from the rotor shaft. An armature current is supplied through a plurality of brushes (these typically being arranged in a stationary fashion in the prior art) and which are arranged in contact with the rotor supported and revolving commutator, this causing a required current reversal for applying power to the motor in an optimal manner as the rotator rotates from pole to pole (it being noted that the absence of such current reversal would result in the motor braking to a stop).
The stator simulates motion by switching applied current in an overlapping fashion (via the partially overlapping and circumferentially offset sets of coils integrated into the stator inner cylindrical wall). As is further known, the magnetic force created in the stator by energizing the wires or coils is opposed by the armature current supplied rods embedded within the rotor, such that the force of the magnetic field generated in the stator in the multi-phase (staged) fashion results in the driving the current in the rotor supported rods (and therefore the rods and rotor as well) at a right angle to the magnetic field induced, thereby rotating the magnetically suspended (air gap supported) rotor and output shaft at a desired speed without the necessity of any moving components.
In this fashion, magnetic fields are formed in both the rotor and the stator, with the product of these giving rise to the force generated driving torque applied to the (typically inner concentrically supported) rotor. As is further understood, one or both of these magnetic fields (as explained further by Faraday's Law and associated Lorentz Forces Law) must be made to change with the rotation of the motor, such as accomplished by switching the poles on and off at the correct time intervals or by varying the strengths of the poles.
Additional variations of more recent AC electric motors further include either synchronous or asynchronous motors (this again being based upon the speed of rotation of the magnetically generated field under Faraday's Law). In particular, a synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the AC and resulting magnetic field which drives it (i.e. exhibiting zero slip under typical operating conditions). In contrast, induction style motors must slip to produce torque and which operate under the principle of inducting electricity into the rotor by magnetic induction (as opposed to by direct electrical connection).
Additional known features include a commutator which is defined as a mechanism used to switch the input of certain AC and DC machines and consisting of slip ring segments insulated from each other and from the electric motor's shaft. In this application, the motor's armature current is supplied through an arrangement of stationary brushes in contact with the (typically) revolving commutator, which causes the required current reversal and applies power to the machine in an optimal manner as the rotor rotates from pole to pole.
Building upon the above explanation, and in an alternate generator application, the rotary shaft is again the input of the rotation by means of an outside work source and, upon being rotated, the configuration of the above-described coils passes by the magnets to create an electrical charge (or field) that becomes the output power variable. An induction generator or asynchronous generator is a type of AC electrical generator that uses the principles of induction motors to produce power.
Induction generators operate by mechanically turning their rotor faster than the synchronous speed, giving negative slip. A regular AC asynchronous motor usually can be used as a generator, without any internal modifications. Induction generators are useful in applications such as mini-hydro power plants, wind turbines, or in reducing high-pressure gas streams to lower pressure, because they can recover energy with relatively simple controls. To operate an induction generator must be excited with a leading voltage; this is usually done by connection to an electrical grid, or sometimes they are self-excited by using phase correcting capacitors.
Other known generator applications include a dynamo which is an electrical generator that produces direct current with the use of a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter.
Features associated with the commutator include it comprising the moving part of a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. Commutators typically have two or more softer (fixed) metallic brushes in contact with them to complete the other half of the switch. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power similarly. As a switch, it has exceptionally long life, considering the number of circuit makes and breaks that occur in normal operation.
Expanding on the above explanation, and as is further known, a commutator consists of a set of copper segments, fixed around the part of the circumference of the rotating machine, or the rotor, and a set of spring loaded brushes fixed to the stationary frame of the machine. Two (or more) fixed brushes connect to the external circuit, either a source of current for a motor or a load for a generator.
Each conducting segment on the armature of the commutator is insulated from adjacent segments through the use of an appropriate material. Many other insulating materials are used to insulate smaller machines; plastics allow quick manufacture of an insulator, for example. In other applications, the segments are held onto the shaft using a dovetail shape on the edges or underside of each segment, using insulating wedges around the perimeter of each commutation segment.
As is further known in the art, a commutator is also a common feature of direct current rotating machines. By reversing the current direction in the moving coil of a motor's armature, a steady rotating force (torque) is produced. Similarly, in a generator, reversing of the coil's connection to the external circuit provides unidirectional (i.e. direct) current to the external circuit.
Without a commutator, a dynamo becomes an alternator, which is a synchronous singly fed generator. Alternators produce alternating current with a frequency that is based on the rotational speed of the rotor and the number of magnetic poles.
Automotive alternators produce a varying frequency that changes with engine speed, which is then converted by a rectifier to DC. By comparison, alternators used to feed an electic power grid are generally operated at a speed very close to a specific frequency, for the benefit of AC devices that regulate their speed and performance based on grid frequency. When attached to a larger electric grid with other alternators, an alternator will dynamically interact with the frequency already present on the grid, and operate at a speed that matches the grid frequency.
Typical alternators use a rotating field winding excited with direct current, and a stationary (stator) winding that produces alternating current. Since the rotor field only requires a tiny fraction of the power generated by the machine, the brushes for the field contact can be relatively small. In the case of a brushless exciter, no brushes are used at all and the rotor shaft carries rectifiers to excite the main field winding.
The armature component of the device must carry current so it is always a conductor or a conductive coil which is oriented normal to both the field and to the direction of motion, torque (rotating machine), or force (linear machine). The armature's role is twofold, the first being to carry current crossing the field, thus creating shaft torque in a rotating machine or force in a linear machine (e.g. motor mode), the second role being to generate an electromotive force (EMF).
In the armature, an electromotive force is created by the relative motion of the armature and the field. When the machine acts in the motor mode, this EMF opposes the armature current, and the armature converts electrical power to mechanical torque, and power, unless the machine is stalled, and transfers it to the load via the shaft.
When the machine acts in the generator mode, the armature EMF drives the armature current, and shaft mechanical power is converted to electrical power and transferred to the load. In an induction generator, these distinctions are blurred, since the generated power is drawn from the stator, which would normally be considered the field.
Applications of electro-magnetic motor and generator assemblies in the patent art include the permanent magnet motor generator set of Strube, US 2010/0013335, which teaches a method of utilizing unbalanced non-equilibrium magnetic fields to induce a rotational motion in a rotor, the rotor moves with respect to the armature and stator. A three tier device (armature, rotor, and stator) has the armature and stator being fixed in position with the rotor allowed to move freely between the armature and stator.
To induce a rotational motion, the rotor, in its concave side uses unbalanced non-equilibrium magnetic fields created by having multiple magnets held in a fixed position by ferritic or like materials to act upon the magnets imbedded in the armature. The rotor, in its convex side has additional unbalanced non-equilibrium magnets and additional pole pair magnets to create a magnetic flux that moves with the moving fixed position fields to cut across closely bonded coils of wire in the stator to induce a voltage and current that is used to generate electrical power. Multiple permanent magnets of varying strength are geometrically positioned in multiple groups to produce a motive power in a single direction with the remainder of the unbalanced magnetic flux positioned and being used to cut across the coils of wire to produce continuous electric power.
Hasegawa, US 2014/0197709, teaches an assembly conducting wire for a rotary electric machine winding which includes a plurality of bundled wires, these being twisted in a circumferential direction, with the wires being welded together at a predetermined distance. US 2007/0096580, to Ketteler, teaches a stator for a three phase current electric machine such as for motor vehicles and which consists of a winding support having grooves and teeth. The windings are arranged in the grooves and the winding support consists of a plurality of identical segments which, after being wound, are shaped into a circular ring. The segments are then inserted into a cylindrical housing and, with their windings, form the cylindrical stator.
Liao, U.S. Pat. No. 7,965,011, teaches a brushless DC motor structure with a constant ratio of multiple rotor poles to slots of the stator and which is characterized primarily by forming the stator of the motor by multiple ferromagnetic silicon steel sheets, where the ferromagnetic silicon steel sheets are provided with the multiple slots whose number is a multiple of 15, and the stator of the motor is formed by windings of the three phases, X, Y, and Z. Each phase includes 2 to 4 phase portions and each group has 5 slots. The rotor of the motor is made up of a plurality of arced magnets which are fixed orderly and equally along a ferromagnetic steel ring, and the radial direction of each arced magnet is opposite to that of the adjacent magnetic poles. An arced magnet represents a magnetic pole, and the number of the magnetic poles is a multiple of 14 or 16, such as for reducing the cogging torque of the motor.
WO 2012/017302, to Kamper/Stellenbosch University, teaches an electrical energy conversion system which is particularly suited for use in wind energy conversion systems. A pair of magnetically separated permanent magnet machines are linked by a freely rotating rotor housing permanent magnets. The first machine is typically a synchronous generator, and the second an induction generator. The synchronous generator has a stationary stator which is connectable to an electrical system such as an electricity grid, and the induction generator has a rotor which is connectable to a mechanical drive system such as a wind turbine.
Kamper, US 2013/0214541, teaches an electrical energy conversion system which is particularly suited for use in wind energy conversion systems. The system includes two magnetically separated permanent magnet machines linked by a freely rotating rotor housing permanent magnets. The first machine is typically a synchronous generator, and the second an induction generator. The synchronous generator has a stationary stator which is connectable to an electrical system such as an electricity grid, and the induction generator has a rotor which is connectable to a mechanical drive system such as, for example, a wind turbine.
Prucher, U.S. Pat. No. 8,247,943 teaches a radial gap motor/generator having a thin annular array of magnets mounted for rotation to a stator in a radially spaced relation to at least one thin annular induction structure fixed to a stationary stator may be air or liquid cooled. The motor has at least radial gap between a magnetic core and the array and may include multiple gaps and multiple annular induction structures to increase the overall power density of the system.
An example of a planetary geared motor and dynamo is shown in Mizushima, U.S. Pat. No. 8,084,912, and which includes provision of planetary gear dynamo for reducing inverse torque when the functioning in a generator mode. Palfai, 2013/0237361, teaches a planetary gear assembly including a ring gear configured for connection to a rotor of an electric motor when in a first position and configured for connection to a housing of the electric motor when in a second position. A sun gear is configured for connection to the housing when the ring gear is in the first position and configured for connection to the rotor when the ring gear is in the second position. A plurality of planet gears are configured to mesh with the ring gear and the sun gear.
Also referenced are the brush holder clip to commutator assemblies shown in each of connector for motors and generators provided in the form of an integral V-shaped spring steel member having an electrical connector extending one of the legs thereof and opposite an apex of the clip and connector. The housing containing the commutator has a slot therein through which the brush holder passes. The V-shaped clip and connector is inserted into the slot and wedged between the brush holder and an edge of the slot. The clip and connector is electrically conductive and communicative with the brush holder and is adapted for mating interconnection with a wire or other conductor.